JPH01221602A - Two-beam interference type linear encoder - Google Patents

Abstract

PURPOSE:To obtain the linear encoder which measures the length of a body, the depth of a hole, a movement distance, etc., with high accuracy by utilizing the principle of a two-beam interferometer, specially, a Mickelson interferometer. CONSTITUTION:The moving-side reflection system 14' of the two-beam interference type linear encoder 20A consists of reverse traveling reflectors, e.g. corner cubes 14B, 14C, and 14D and a plane mirror 14E. The reverse traveling reflectors 14B and 14D are arranged in a Y direction on a linearly movable rack 14A which is moved linearly by a driving mechanism while having their reflecting surfaces on the sides of while luminous flux and laser luminous flux which are split by a beam splitter 11. The fixed corner cube 14C and fixed plane mirror 14E are arranged in the Y direction outside the moving rack 14A and photodetect and reflect 2nd luminous flux which is reflected by those corner cubes 14B and 14D toward the corner cube 14D. Interference figures (a) and (b) are obtained by detectors 28 and 32. The interference figure (a) of the laser light can be utilized as an accurate scale for measuring a movement distance, etc.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention utilizes the principle of two-beam interference, particularly a Michelson interferometer, to determine the length, thickness, hole depth, linear displacement, position, and The present invention relates to a linear encoder that is useful for measuring the optical spectrum of a light source, etc., and performing Fourier transform spectroscopy over a wide wavenumber range of the optical spectrum of a light source.

[Prior art] As shown in Figure 3, the Michelson interferometer uses a single light source (
(not shown) is split into two beams traveling in the X and X directions perpendicular to each other through a beam splitter 11, and each split beam is returned to its original direction by a fixed reflector 12 and a movable reflector 14. It is configured so that it undergoes retrograde reflection, multiplexes and interferes both beams on the beam splitter 11, forms an image on the detector 18 using the concave mirror 16, and detects the light intensity of the interference pattern due to the optical path difference between the two beams. be.

Therefore, when a reflective object to be measured is inserted into the - of the two beam paths split by the beam splitter of the Michelson interferometer, the change in the interferogram caused by the optical path difference between the two beam paths can be detected. , the length and thickness of an inserted object, or the depth of a hole can be measured with wavelength-level accuracy.

Furthermore, when the movable reflector 14 of the above-mentioned Michelson interferometer is displaced in accordance with the movement of the measurement target, the change in the interferogram due to the optical path difference before and after the movement of the movable reflector 14 is measured to determine the moving distance. Can be done.

Furthermore, in order to perform Fourier transform spectroscopy of the sample transmitted light,
Conventionally, a Fourier transform spectrometer using a Michelson interferometer, having the configuration shown in FIG. 4, has been used.

This Michelson interferometer is composed of a main interferometer 0 and a linear encoder 20, which share a movable reflector 14.

The main interferometer 10 has the same configuration as the Michelson interferometer shown in FIG. The movable reflection system divides each divided beam into two beams traveling in the X and X directions perpendicular to each other, and scans each divided beam at a constant speed by a fixed reflector 12 and a drive system (not shown)! 4 reflected back to the original direction, and beam splitter 1! The waves are combined by the concave surface m1
6 to form an image on a detector 18 and measure an interference pattern (interferogram) based on the optical path difference between the two light beams.

On the other hand, the linear encoder 20 has a reflective surface on the side opposite to the main interferometer side of the movable reflector 14, and receives a wavelength-stabilized laser light source 22, such as a He-N e laser, and a white light source, such as a Xe lamp 30. A beam splitter 11 that splits the emitted parallel light beam into the X direction and the Beam splitter for luminous flux! It is composed of interference light intensity detectors 28 and 32 that respectively detect the laser beam and the white beam combined in (1).

Since the interferogram from the detection 328 is a sine wave and the optical path difference can be measured accurately, it can be converted into a comb-shaped signal indicating a sample point and used as a sample signal. Furthermore, since the light intensity of the interferogram obtained by the detector 32 has a strong peak when the optical path difference in the linear encoder is zero, it can be used to determine the reference point of the movable reflector 14.

Therefore, 1. The main interferometer 10 measures the interference pattern due to the optical path difference of the two-split beam over the entire spectrum of the light to be measured in synchronization with the sample signal of the detector 28 of the encoder 20, and detects 'a30'. By processing the data using the reference point detected by the sample signal as the reference point of the sample signal, the light incident on the interferometer can be subjected to Fourier transform spectroscopy.

[Problems to be Solved by the Invention] However, since the encoder 20 is reflected backward once by only one movable reflector 14, the optical path difference of the light beam traveling toward the movable reflector 14 is different from that of the movable reflector 14. 14, and the measurement accuracy of linear displacement is only about half the wavelength of a laser beam, which is a limit.

Therefore, even if the length, thickness, hole depth, moving distance, etc. of an object are measured using the linear encoder shown in FIG. 3, it is not possible to measure with high resolution.

Therefore, it is not required to measure the length, thickness, and moving distance of an object with high precision.

Also, in the case of the Fourier transform spectrometer using the linear encoder 20 shown in FIG. 4, it is not possible to measure the spectrum of the target light over a wide wave number range based on the above-mentioned reason.

In view of the above-mentioned problems, it is an object of the present invention to utilize the principle of a two-beam interferometer to measure the length, thickness, depth of a hole, moving distance, etc. of an object with high precision, and to measure the light to be measured. An object of the present invention is to provide a linear encoder that enables Fourier transform spectroscopy over a wide wavenumber range.

[Means for Solving the Problems] In order to achieve this object, the two-beam interference type linear encoder according to the present invention includes a laser light source and a laser beam emitted from the laser light source that travels in two directions perpendicular to each other. A beam splitter that splits the beam into two beams, and the second one of the two beams split by the beam splitter! A fixed reflector is provided in the optical path of the luminous flux and reflects the incident first luminous flux backward toward the beam splitter, and a fixed reflector is provided in the optical path of the second luminous flux of the two luminous fluxes split by the beam splitter. a movable retroreflector that is movably arranged along the traveling direction of the second luminous flux and reflects the incident luminous flux retrogradely in a direction opposite to the incident direction; and a fixed retroreflector that is arranged to reflect the incident light flux in a direction opposite to the direction of incidence.
a movable-side reflection system that causes a second light beam incident on the movable retroreflector to be reflected back from the movable retroreflector through the fixed retroreflector and back to the movable retroreflector; a detector for combining and interfering the first and second beams reflected backwards toward the beam splitter from the fixed reflector and the movable reflection system, respectively, by the beam splitter, and measuring the light intensity of the resulting interference pattern; The method is characterized in that the linear displacement of the movable retroreflector is measured from the change in light intensity of the interference pattern of the laser beam.

Here, the reflector includes not only a mirror surface but also a reflector using a prism.

[Example] (1) One example An embodiment of the present invention will be described based on the drawings.

FIG. 1 is a block diagram of an embodiment of a two-beam interference type linear encoder having a Michelson interferometer structure.

This two-beam interference type linear encoder 20A corresponds to the configuration of the Fourier transform spectrometer linear encoder 20 shown in FIG. Linear encoder 2 in Fig. 1 and Fig. 4
Components that are the same as those in FIG.

In Fig. 1, 14' is a movable reflection system, including a retroreflector,
For example, corner cube (reflector or prism) 14B
It consists of S 14G, 14D and a plane mirror 14E.

The retroreflectors 14B and 14D are mounted on a pedestal 14A that is linearly movable in the X direction by a drive mechanism (not shown), and reflect the white light beam and laser beam split by the beam splitter 11 in the Y direction with their reflective surfaces facing east. It is located.

The fixed corner cube 14G and the fixed plane mirror 14E are
It is arranged along the Y direction outside the movable frame 14A,
These receive the second light beam reflected by the corner cubes 148 and 14D, and reflect it toward the corner cube 14D.

In this embodiment, the retroreflector 1 constituting the movable reflection system 14
Since corner cubes are used as 4B, 14C, and 14D, even if some shaking occurs when the pedestal 14A is moved linearly in the
It is possible to accurately reflect back in the direction.

Detectors 28 and 32 produce interferograms a and b, respectively, as shown in FIG. &° is an interferogram obtained by the detector 28 of the conventional device shown in FIG. Since the interferogram a of the laser beam is sinusoidal, it can be converted into a comb shadow signal that specifies a sample point, and can be used as an accurate yardstick for measuring moving distance, etc. In addition, in the white light interference pattern, the optical path difference in the linear encoder 2OA is 0.
Since a strong peak occurs when
It can be used to determine the reference point.

In this embodiment, the moving distance X of the movable frame 14 in the X direction and the optical path difference between the fixed movable mirror 14E and the beam splitter 11 have a relationship of L=8x, and the optical path difference is made 8 times the moving distance. be able to. Since the resolution of a linear encoder is proportional to the optical path difference with respect to the moving distance, by using a configuration like this example, the resolution of the linear encoder can be increased.
It is possible to precisely measure the length of an object and the distance traveled by its thickness. By using such a linear encoder in a Fourier transform spectrometer, the maximum measurement wave number range of a conventional Fourier transform spectrometer can be increased to 32.000 cm-', compared to only O ~ 7950 c@-'. I was able to do that.

(2) Expansion Note that the present invention includes various other modifications.

For example, in this embodiment, not only laser light but also white light is passed through the same optical system, but for white light, the distance between the laser light source 22 and the white light source 30 is Alternatively, another plane mirror may be arranged on the pedestal 14A, and the white light beam may be reflected by this mirror and made to travel backward toward the beam splitter li.

In addition, although this example shows an example in which laser light and white light are used as light sources, it is also possible to measure the distance traveled by a moving object by using only laser light without using white light. good.

Furthermore, in this embodiment, an example in which a corner cube is used as the retroreflector constituting the movable reflection system has been described, but a right-angled trigonal mirror, a composite retroreflector, or the like may be used instead.

Furthermore, a corner cube may be used instead of the fixed plane *14B, and the light beam may be incident on the vertex thereof.

Furthermore, the movable side reflection system is not limited to four reflectors as long as the same number of retroreflectors are provided on the fixed side and the movable side.

[Effects of the Invention] In the two-beam interference type linear encoder according to the present invention, the movable reflection system includes a movable retroreflector that retrogradely reflects the incident light flux in a direction opposite to the direction of incidence, and the movable retroreflector. It consists of a fixed reflector that is placed with its reflective surfaces facing each other and reflects the incident light beam backwards in the incident direction and the reflection direction, and the light beam incident on the movable backward reflector is fixed from the movable backward reflector. Since the light passes through the reverse reflector and is reflected back to the movable reverse reflector, the optical path difference with respect to the moving distance of the object to be measured is more than twice that of a conventional linear encoder, dramatically increasing the resolution and It has the excellent effect of being able to measure the length, thickness, depth of holes, and travel distance with high precision.

Further, when the linear encoder of the present invention is used in a Fourier transform spectrometer, it has the excellent effect of making the maximum measurement wave number range more than twice as wide as that of the conventional method.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a two-beam interference linear encoder according to an embodiment of the present invention, and FIG. 2 is a comparison of the interference patterns of laser light and white light measured by the two-beam interference linear encoder with a conventional example. FIG. 3 is a block diagram of a conventional linear encoder, and FIG. 4 is a block diagram of a conventional linear encoder used in a Fourier transform spectrometer. lO: Main interferometer of Fourier transform spectrometer 11: Beam splitter 12: Fixed reflector 14: Movable reflector 14°: Movable side reflection system 14A: Movable frame 14E% 14E: Fixed retrograde reflector 14B, 140: Movable Reverse reflector 22: Laser light source 28: Laser light interference light intensity detector 30: White light source 32: White light interference light intensity detector

Claims (1)

[Claims] A laser light source (22); a beam splitter (11) that splits the laser beam emitted from the laser light source (22) into two beams traveling in two directions perpendicular to each other; and the beam splitter (11). ), of the two luminous fluxes divided by
a fixed reflector (12) that reflects the luminous flux of the beam backward toward the beam splitter (11);
Among the two light beams divided by 1), a movable member is disposed in the optical path of the second light beam in a movable manner along the traveling direction of the second light beam, and reflects the incident light beam backward in a direction opposite to the direction of incidence. Reverse reflectors (14B, 14D) and fixed reverse reflectors that are arranged so that their reflecting surfaces face the movable reverse reflectors (14B, 14D) and reflect the incident light flux backward in a direction opposite to the direction of incidence. reflectors (14C, 14E), and the second wave incident on the movable retroreflector (14B, 14D)
A movable side reflection in which a luminous flux of system (14'), the fixed reflector (12) and the movable reflection system (14')
The first and second beams of light reflected backward from the beam splitter (11) are sent to the beam splitter (11).
11), and a detector (28) that measures the light intensity of the resulting interference pattern, and detects the movement of the movable retroreflector (14B, 14D) from the change in the light intensity of the interference pattern of the laser beam. A two-beam interference type linear encoder that measures linear displacement.